Based on the existing structural design code for pressure vessel and nuclear light water reactor power stations, situations for metallic structures in hightemperature gas-cooled reactors (HTGRs) are described for those metallic structures that mainly operate in temperature ranges of time-independent and time-dependent materials properties. The ASME Code Case N 47 is critically reviewed. For advanced HTGRs with components for operating temperatures >800°C, no nuclear accepted structural design code exists. The status of the ongoing work for the basis of those codes is given with the main emphasis on the situation in the Federal Republic of Germany.